Titled Method and system for making a line of required length using ink jet

FIELD OF THE INVENTION

The invention relates to ink jet technology.

BACKGROUND OF THE INVENTION

Flat panel display manufacture currently uses inkjet for printing low resolution layers. Other layers in the device require a much higher resolution, and are therefore not suitable for conventional inkjet heads. Using inkjet for these layers can lead to a great simplification of the process and to considerable cost reductions.

InkJet is currently limited in its ability to print very fine features in the order of lOμm. This is due to various reasons, e.g. drop size, spot size on paper, interactions between the drops and the substrate and among the drops on the substrate. Fig. Ia shows a line created using ink jet printing by sequentially juxtaposing ink droplets 10 along a line. Owing to the circular shape that the droplets 10 assume on the substrate and the fact that they are evenly spaced, the result on drying as shown in Fig. Ib will be a line 11 whose length is an invariable function of the rate at which drops are deposited.

Furthermore, attempting to use conventional ink-jet techniques, particularly when very thin lines are required, requires expensive, off-line correction of defects such as pin holes which can render a line to be non functional. This, of course, is all the more critical when the lines are used to form electrically conductive tracks in a PCB since such pin holes may be manifested as open circuits.

In all ink jet printers, the print resolution determines the inter-droplet spacing and in the prior art, the inter-droplet spacing is a quantum of length such that the length of any line drawing with an ink jet mechanism must always be an integral number of inter-droplet spacing quanta. Therefore, if it is required to draw a line which is not an integral number of inter-droplet

spacing quanta, the only way it can be done in a manner that will achieve the extremely fine tolerances required with integrated circuit fabrication is to draw the line longer than is required and then remove the excess material. Although this is typically done using masking technology, it can also be done on the fly using a laser, which cures the ink as it is deposited but must, of course, be switched off when the requisite quantity of ink has been dropped to achieve the required length, thus allowing the uncured ink to be washed away. This allows fine adjustment of the length of the line but requires that the laser be switched off when exactly the right length of line has been cured so as thereby to control the length of the line (after rinsing) very precisely.

Owing to the simplicity of ink-jet techniques, their profusion and low- price, it would be a significant benefit if ink-jet technology could be used to produce the fine lines required for the fabrication of electronic devices without being subject to the drawbacks described above. WO2005/022969 entitled "Method and System for Creating Fine Lines

Using Ink Jet Technology" discloses improved inkjet technology that addresses this problem in the cross-scan direction.

SUMMARY OF THE INVENTION

It is an object of the present disclosure to provide an improved method and system for producing fine lines of specified length required for the fabrication of electronic devices using ink-jet technology.

It is a specific object of the disclosure to provide a method and system that complements the approach disclosed in above-mentioned WO2005/022969 by offering variable resolution in the scan direction. To this end, the complete contents of WO2005/022969 are incorporated herein by reference.

This object is realized in accordance with one aspect of by a method and system that enables very fine features to be printed using an inkjet device in combination with an auxiliary optical system.

Thus, in accordance with another aspect there is provided a method for making with an ink jet nozzle a geometry of desired in scan length on a substrate, the method comprising: dropping successive droplets of a material on to the substrate so as to form said geometry; and adjusting a frequency of the ink jet nozzle so as to vary an inter-droplet spacing so that the desired in scan length may be formed with an integral number of droplets.

In accordance with another aspect there is provided an inkjet printing system comprising: at least one print nozzle for dispensing successive droplets of a material on to a substrate, and a controller coupled to the at least one print nozzle the control being configured for adjusting a rate at which the at least one print nozzle is addressed so as to vary a gap between adjacent droplets.

The disclosure thus allows lines of specified in scan length to be drawn with an inkjet printer without requiring either masking technology and by obviating the need to constantly switch on and off a laser, which cures the ink as it is deposited but must be switched off when the requisite quantity of ink has been dropped to achieve the required length, thus allowing the uncured ink to be washed away.

Thus, it is possible to cure the line on the fly without switching the laser off at all since, when the requisite length of line has been printed, no more ink is deposited until the start of the next line and in the interim period, the laser merely strikes the substrate with no deleterious effect.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the disclosure and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Figs. Ia and Ib are pictorial representations of a line formed of a series of juxtaposed ink droplets using conventional ink jet technology;

Fig. 2 is a pictorial representation showing a system according to the invention; Fig. 3 shows pictorial representations of successive stages in the formation of lines produced by an ink jet assisted process followed by curing;

Fig. 4 shows pictorial representations of successive stages in the formation of lines produced by IR ablation of juxtaposed ink jet droplets! and

Fig. 5 is a pictorial representation showing successive stages in the formation of lines produced by addressing inkjet nozzles at varying frequency.

DETAILED DESCRIPTION OF EMBODIMENTS

The principle of this technique is to reduce the printed drop size in both directions ^:

• Most importantly, in the scan direction accurate features may be printed by addressing the inkjet head at a much higher resolution than the basic printing resolution. This allows a line to be marked of any desired length using an integral number of ink droplets.

• In the cross"scan direction, the drop width is reduced by selectively eliminating the edges of the drop by optical means (e.g. by curing or softening)

Cross-scan configuration

The system consists of an inkjet printing module and an optical module (e.g. a radiation source). Both modules share the same carrying frame, and they are aligned with one another. Each radiation source is aligned with a specific nozzle of the print head. The radiation source trails (i.e. is located downstream of) the printing head, and is kept constantly ON, focused on the printed drops. Each drop that is ejected by the nozzle is therefore treated optically by the radiation source right after printing (Fig. 2). As an example, it

is possible to use a focused UV laser source, in conjunction with a UV curable liquid, to cure a part of the printed drop. When a series of drops is ejected, the result is a fine line, with straight edges (Fig. 3).

The source for the UV radiation can be a standard UV lamp coupled into a thin optical fiber, which serves as a light guide. At the exit from the fiber the light is focused on the printed surface using a lens. This method enables a single source to be split into a multitude of optical channels. The material disposed by the inkjets may be ink and may be applied only to discrete areas of the substrate that are each sufficient to accommodate one or more lines within their respective boundaries. The material may be a photosensitive curable material that is curable by UV laser light, for example. The photosensitive curable material may be exposed to light via a mask so as to cure the material corresponding to the geometry.

The photosensitive curable material may be applied to an active layer on a substrate, there being further included: exposing the photosensitive curable material to light via a mask so as to cure the material corresponding to said geometry. flushing the uncured areas of the photosensitive curable material so as to reveal the geometry; etching those areas of the active layer that are not covered by cured material; and removing the pattern made of the cured material.

The photosensitive curable material may be applied only to discrete areas of the active layer on the substrate that are each sufficient to accommodate one or more geometries within their respective boundaries.

Another optional process is the removal of the drop edges, by softening or ablating radiation. This way, two radiation sources may be required for the removal of either edges of the printed drop (Fig. 4).

It is important to note that the radiation source remains on throughout the printing process. There is no need for switching it off during printing, unless an in-scan modulation is required.

The redundant area of the pattern may be removed by curing an area of the pattern that defines said geometry and removing all material that is not cured. The geometry may be cured using a laser beam. The droplets may be cured directly after their placement on the substrate or after the ink pattern is completely formed.

The redundant area of the pattern may be removed by ablating at least one redundant area of the pattern that surrounds the geometry. A laser may be used to create controlled and precise ablation. An area of the pattern that defines the geometry may also be cured.

The droplets may be monitored and a missing or incompletely formed droplet may then be perfected. This may be effected by one or more auxiliary ink jet printer heads. Droplets may be duplicated so as to reduce the likelihood of a missing or incompletely formed droplet. This may be done by one or more auxiliary ink jet printer heads.

The disclosure also include s^ inkjet printing a first geometry with first material so as to form a first line of the desired in scan length, inkjet printing a second, substantially parallel, geometry of second material so as to overlap the first line so as to form an overlapping second line of the desired in scan length; the first and second lines being formed of materials that react on contact so as to cure the lines where they contact while having no effect on those areas of the two lines that do not overlap; and flushing the first and second materials that have not cured.

Such an approach may include: inkjet printing substantially parallel non-contiguous first and second lines formed of a first material that may be flushed from the substrate,'

inkjet printing a third, substantially parallel, line formed of a second material so as to overlap the first and second lines so as to cover an intervening space between the first and second lines; curing the second material in the space between the first and second lines so that it adheres to the substrate,' and washing the substrate so as to flush the first and second lines together with remaining portions of the third line with which they overlap.

There may also be included: inkjet printing a first area with first material to form a first primary color, inkjet printing a second area with a second material to form a second primary color so as to overlap the first primary color so as to form an overlapping area; the first and second materials being such that they react on contact so as to turn black.

In scan configuration

A high resolution in the scan direction is obtained by changing the addressing frequency of the print head. By having a basic frequency higher than the printing frequency it is possible to print accurate details. For example: the normal printing frequency of the print head is 5KHz, corresponding to a drop every 42μm (600dpi). In order to accurately control the length of the printed line, the electronic frequency may be changed to 15KHz, corresponding to a drop every 14μm. The normal drop ejection will still be every 42μm, however, in order to begin or terminate fine lines accurately, the first and last drops may be ejected in gaps of 14μm from their adjacent drops. This will produce accurate line lengths as necessary (Fig. 5.).

An inkjet printing system may comprise • at least one print nozzle for dispensing successive droplets of a material on to a substrate, and

a controller coupled to the at least one print nozzle configured for adjusting a rate at which the at least one print nozzle is addressed so as to vary a gap between adjacent droplets.

Such a system may further comprise a laser disposed downstream of the print nozzle for curing or drying a pattern formed within a boundary of successive droplets.

Summary and conclusion

The method outlined above enables an image to be printed with an inkjet head at a much higher resolution than the basic resolution of the print head. This is done by adding an optical system for the cross-scan direction and changing the addressing frequency for the in-scan direction. The additional optical system is relatively simple and does not require complicated control hardware to modulate it. The system may be used for applications requiring very high resolution, where hitherto-proposed solutions are more complex and expensive. This is especially useful for applications of flat panel manufacture, where a single inkjet system can be used instead of expensive lithographic methods.